Waste disposal is a major global problem in the world today. The escalating population, coupled with the use of more polymeric materials, has resulted in the creation of large landfills that are filled with non-biodegradable materials. Efforts have been made to try to create more biodegradable materials. These efforts are primarily focused on preparing polymers that degrade when exposed to sunlight or to manufacture materials from starch and other plant proteins that will degrade in a relative short period of time under normal environmental or composting conditions of temperature, humidity, and the action of microorganisms.
Bassi et al. (U.S. Pat. No. 5,665,152) propose a method of forming solid, non-edible biodegradable, grain protein-based articles. A grain protein formulation is heated to a maximum temperature of up to about 80° C. to create a substantially homogeneous and flowable mixture which can be formed into solid biodegradable articles. The formulation includes from about 20-85% by weight of grain protein, from about 5-75% by weight starch, up to about 14% by weight water, from about 10-40% by weight plasticizer, and at least about 0.01 by weight of a reducing agent such as sodium bisulfite for cleaving disulfide bonds present in the grain protein. Optional ingredients such as fillers, fiber, lubricant/mold release agents and colorants can also be used. The formulations are heated under moderate temperature conditions, usually with shear, to create a substantially homogeneous and flowable formulation. Thus, in the context of injection molding, the preferred temperature conditions of molding assure essentially complete protein denaturation. Reducing agents are an important component of the formulations because they drastically improve the flow and mixing of the grain protein and also serve to enhance the final products in terms of appearance, mechanical properties and moisture resistance.
Rayas et al. (U.S. Pat. No. 6,045,868) describe a method wherein grain flour proteins are crosslinked with aldehydes and bleached with a bleaching agent to form crosslinked transparent polymers used as films for packaging. The process uses ethanol and water for the extraction at acidic or basic pH's and optionally heating with or without a reducing agent to provide the polymer to be bleached and crosslinked. More specifically, the method involves the separation of biopolymeric materials from grain flours to make plastic films by a solubilization process with selected solvents. Once separated, the grain flour biopolymers are crosslinked and plasticized to form a film-forming solution. A heating process is preferred in order to concentrate the film-forming solution and denature the flour protein prior to crosslinking and bleaching so that more protein interactions occur when the film is dried and stronger films are formed. The heating process must be in the range of 30° C. up to the boiling point of the solution, with a preferred range of 60° C., up to the boiling point.
Woerdeman et al. (WO 2004/029135 A2) describe a gluten polymer matrix, with tunable material properties, produced by using polythiol-containing molecules during the preparation process. The process for preparing the gluten polymer matrix comprises dispersing or mixing gluten in the presence of polythiol-containing molecules or combining gluten with polythiol-containing molecules in a gluten-dispersing mixture. In another embodiment of the invention, the process also comprises an isolation step which consists of precipitating the proteins or a fraction thereof, for example by changing the pH of the dispersion, by changing the concentration of one of the solvents used or by changing the ionic strength of the mixture. When compression-molding is performed, a minimum temperature of 100° C. and a minimum pressure of 2 bars for a minimum of 1 minute is required.
Aung (U.S. Pat. No. 5,279,658) describes a composition suitable for forming into shaped articles comprising flour, starch, and water. The flour, starch and water are each present in an amount such that the composition is rigid and stable over a predetermined temperature range. The composition preferably contains 40-80% by weight flour, 20-60% starch and 15-25% water. The flour and starch are obtained from natural cereal sources, such as corn, rice, potato, tapioca and wheat. The composition may be in pellet form or any other form suitable for employing in a process for preparing shaped articles. A mixture of flour and starch are prepared wherein the flour and starch have a uniform particle size. The mixture is heated and mixed under a sufficient pressure temperature and moisture content and for a sufficient period of time such that when the pressure is decreased the mixture expands to form a composition which when cooled is rigid and stable over a predetermined temperature. In the cooking phase, the sifted mixture, water and any coloring and flavoring agents are fed into an extrusion cooker at a feed rate of 2-7 Kg/hour and a nozzle ratio of 2:4 with a single or twin screw rotating at a speed of 90-220 rpm. The dough is mixed, kneaded and cooked with a moisture content of 15-35% at a temperature of 120°-200° C. and pressure of 200-300 psi. The pressure is reduced by venting resulting in expansion of the dough. The expanded hot dough is pressure injected into a form press which has a water-cooled die mold. The expanded hot dough fast cools in the form press at the surface of the cold die mold. The expanded packaging material is stamped to the correct thickness in the form press. The formed packaging material may then be coated with a water repellant material, dried in an oven and cooled in a cooling chamber.
An object of the present invention is to provide a low temperature molding process for preparing solid biodegradable articles from wheat gluten.
Another object of the present invention is to provide a low temperature molding process that involves drying but not cooking of the wheat gluten, such that the primary structure of the wheat gluten protein remains essentially unchanged.